1. Field of the Invention
The present invention relates to a magnetic disk read/write circuit and, particularly, to a magnetic disk read/write circuit capable of improving S/N ratio of a read signal in such as a magnetic disk tester or a magnetic head tester, which uses a MR (Magneto Resistive) head, a GMR (Giant Magneto Resistive) head and a TMR (Tunnel Magneto Resistive) head as read heads.
2. Description of the Related Art
As a magnetic disk read/write head for a hard disk device, the so-called complex magnetic head including an inductive head (thin film head) as a write side head and a MR head, a GMR head and a TMR head as read side heads, all of which are mounted on a single slider, is widely used recently. Under the circumstance, the recent magnetic disk tester for testing a hard magnetic disk or the recent magnetic head tester for testing the magnetic heads uses such complex magnetic read/write head. However, since, with the recent improvement of the recording density of the magnetic disk, the frequency of a read/write signal is increased, the S/N ratio of a read signal is degraded, causing the accuracy of the test to be degraded.
FIG. 4(a) shows a write signal waveform for the inductive head (thin film head) on the write side, FIG. 4(b) shows a state of magnetization of a track on a magnetic disk corresponding to the write signal shown in FIG. 4(a), FIG. 4(c) shows a read signal waveform when the thin film head or the MR head reads the written data from the track of the magnetic disk and FIG. 4(d) shows the read signal waveform with noise.
The read signal waveform usually contains noise as shown in FIG. 4(d) and the larger the influence of noise is the higher the read frequency. Further, since the voltage level of the read signal is lowered with increase of the frequency, precise test becomes difficult.
Recently, in order to improve the efficiency of the test, a number of magnetic disks are used in one tester or the test of magnetic disks or magnetic heads is performed in parallel by arranging a number of test devices in parallel on one test table. In such test system, due to the use of high frequency in recording data, noise is induced in a MR head and a GMR head, which are located in the vicinity thereof and are in reading operation. Such noise is detrimental for the test result. In such case, noise frequencies observed in the MR head and the GMR head is usually even harmonics of the recording frequency and noise on the read signal shown in FIG. 4(d) becomes large.
An object of the present invention is to provide a magnetic disk read/write circuit capable of improving S/N ratio of a read signal from a magnetic head, particularly, a MR head or a GMR head.
In order to achieve the above object, a magnetic disk read/write circuit according to the present invention is featured by comprising a core on which a pair of coils are provided such that signals on the coils become opposite in phase and a read circuit having a first input terminal connected to one of terminals of a read head through one of the coils to receive a read signal from the read head and a second input terminal connected to the other terminal of the read head through the other coil to receive the read signal phase from the read head.
Since the read circuit receives the positive phase read signal and the negative phase read signal from the read head through the coils on the core, which are wound such that the signals supplied to the coils become opposite in phase, noises of the positive and negative read signals overlapped on signal lines as in-phase components, respectively, are cancelled out or restricted by the core.
As a result, it becomes possible to improve the S/N ratio of the read signal from the magnetic head to thereby realize a magnetic disk tester or a magnetic head tester, which can perform a high precision test.
Further, by providing a core having a pair of coils between a write head and a write circuit similarly, a rising and falling of a write signal current becomes substantially symmetrical, so that it is possible to obtain a read signal which is hardly influenced by noise.